Suddenly an idea flashed across Tressidar's mind.
"I'll try it," he thought, and gave an order for the engines to be stopped.
When No. 445 lost way he made tests to ascertain the true direction of the wind. Although it was almost calm when he left Auldhaig, the sub. made the discovery that there was a steady draught from the south-west. He also knew that for the last four hours the tide had been making northwards.
A water-borne Zeppelin, he argued, was to a greater extent under the influence of the wind, and to a lesser extent of that of the tide, although that depended largely upon the area of the submerged portion of the huge fabric. Allowing the airship to have been drifting for four hours, by this time she must be at least sixteen miles from the spot where she dropped, unless in the meanwhile she had sunk.
Accordingly TB 445 made off in a north-easterly direction, the sub. sweeping the sea with his night-glasses with the air of a man who subconsciously feels convinced that his efforts will meet with success.
Shortly after two in the morning a slight mist, accompanied by cold rain and sleet, rendered the searchers' task a most difficult one. Speed was reduced to fifteen knots, and the look-outs doubled, since the little craft was now in the waters frequented by the north-east of Scotland fishing-boats.
"Light on the port-bow, sir," reported one of the crew, as the feeble glimmer of a masthead and port lights loomed through the mirk.
Tressidar telegraphed for "easy ahead," then "stop," at the same time ordering the helm to be starboarded in order to approach the strange craft.
"They're making a deuce of a noise," he soliloquised, as the murmur of a babel of voices was wafted through the night.
Even as he looked the sub. discovered that the beams of the vessel's masthead light were playing upon an immense indistinct mass lying apparently a cable's length to windward. The mass was the envelope of the Zeppelin.